1. Field of the Invention
The present invention relates to a magnetic head that is used for writing data on a recording medium, and more specifically, to a magnetic head having a contact sensor.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and magnetic heads of improved performance have been demanded accordingly. Among the magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the magnetic head is mounted on a slider that flies slightly above the surface of a recording medium. The magnetic head has a medium facing surface that faces the surface of the recording medium.
For a magnetic disk drive, it is desired that the distance between the medium facing surface of the magnetic head and the surface of the recording medium be small and constant in order to prevent the reading and writing capabilities from degrading with increasing recording density.
If the distance between the medium facing surface of the magnetic head and the surface of the recording medium is reduced, however, the medium facing surface becomes more likely to come into contact with the surface of the recording medium. On the other hand, the surface of the recording medium sometimes has minute projections. In such a case, the medium facing surface can come into contact with the projections of the surface of the recording medium, though not with the other areas of the surface. Furthermore, if the surface of the recording medium is wavy, the medium facing surface can come into contact with certain areas of the surface of the recording medium. Since the contact of the medium facing surface with the surface of the recording medium hinders normal read and write operations, it is necessary to avoid such a contact.
To cope with this, the following two methods may be employed to prevent or detect the contact of the medium facing surface of the magnetic head with the surface of the recording medium by using a contact sensor for detecting the contact of the medium facing surface with the surface of the recording medium. A first method is to carry out a test prior to shipment of the magnetic disk drive as a product in order to detect the portion of the surface of the recording medium with which the medium facing surface may come into contact. This makes it possible to control the magnetic disk drive so that the medium facing surface will not come into contact with the surface of the recording medium during the read/write operations of the magnetic head. A second method is to monitor the distance between the medium facing surface and the surface of the recording medium, with the contact sensor allowed to operate all the time during the read/write operations of the magnetic head. The first and second methods may be used in combination.
JP-A-2008-77751 discloses a head slider for inspecting a magnetic disk. The head slider includes: a substrate having a flying surface and an element-forming surface; a heat generating resistor section formed on the element-forming surface of the substrate; and a thermal conductive layer disposed above or below the heat generating resistor section. The heat generating resistor section includes a heat generating resistor layer formed of a material having a predetermined temperature coefficient of resistance, such as metal, and two lead layers for passing an electric current through the heat generating resistor layer. The heat generating resistor layer generates heat when supplied with power via the two lead layers, and thereby causes part of an end face of the slider on the flying surface side to protrude. The protruded part of the end face of the slider may come into contact with or collide with a projection on the magnetic disk surface. In this case, the frictional heat produced by this event increases the temperature of the heat generating resistor layer, thereby changing the resistance of the heat generating resistor layer. This allows for detecting the contact or collision of the protruded part of the end face of the slider with the projection on the magnetic disk surface. The thermal conductive layer is formed of a material having a high thermal conductivity, such as metal. The thermal conductive layer allows the heat from the heat generating resistor layer to be uniformly distributed in the region where the thermal conductive layer is present and a region therearound.
U.S. Pat. No. 7,589,928 discloses a magnetic head that includes a sensor capable of measuring the distance between the magnetic head and the surface of a recording medium on the basis of resistance variations. The sensor is energized, and any resistance variation of the sensor appears as a variation in voltage drop in the sensor. A sudden increase in voltage drop in the sensor allows for detecting that the magnetic head has come into contact with the recording medium.
Now, a case will be contemplated where a magnetic head is provided with a contact sensor that varies in resistance in response to temperature variations. In this contact sensor, a variation in resistance is detected, for example, as a variation in voltage drop. For such a contact sensor, in general, increasing the voltage applied to the contact sensor can improve the performance, such as sensitivity and signal-to-noise ratio, of the contact sensor. On the other hand, however, increasing the voltage applied to the contact sensor increases the current density of the contact sensor and also increases the amount of heat generated by the contact sensor itself. This causes electromigration to become noticeable and results in a reduction in service life of the contact sensor, thus leading to degradation in reliability of the contact sensor.
To address this problem, the inventors of this application contemplated providing a heat sink to be adjacent to the contact sensor. Each of the contact sensor and the heat sink has an end face located in the medium facing surface. The inventors confirmed by simulations that the heat sink thus provided could improve the reliability of the contact sensor when the voltage applied to the contact sensor was increased.
The inventors then discussed the material for the heat sink. A heat sink for typical use may be formed of a material having a high thermal conductivity. For a heat sink that is to be provided adjacent to the contact sensor in a magnetic head, however, some materials may give rise to the following problem due to the method of manufacturing the magnetic head.
Typically, magnetic heads are manufactured by the following method. First, components of a plurality of magnetic heads are formed on a substrate to fabricate a substructure that includes a plurality rows of pre-slider portions. The pre-slider portions are to become a plurality of sliders later. The substructure is then cut to separate the pre-slider portions from each other into a plurality of sliders. When forming the plurality of sliders, the cut surface is polished into the medium facing surface.
In the step of forming the medium facing surface by polishing, the amount of polishing may differ among components of the magnetic head due to differences in materials of the components. Accordingly, the amount of polishing of the heat sink in the step of forming the medium facing surface may become greater or smaller, depending on the material of the heat sink, than the amounts of polishing of the components of the write head section and the read head section. As a result, in the medium facing surface, the end face of the heat sink may be recessed or protruded relative to the end face of each of the write head section and the read head section. Accordingly, the amount of polishing of the contact sensor adjacent to the heat sink may be affected by the amount of polishing of the heat sink, so that the end face of the contact sensor in the medium facing surface may also be recessed or protruded relative to the end face of each of the write head section and the read head section. In such a case, the sensitivity of the contact sensor may be reduced, or the write characteristics of the write head section and the read characteristics of the read head section may deteriorate. More specifically, if the end face of each of the heat sink and the contact sensor is recessed relative to the end face of each of the write head section and the read head section, the sensitivity of the contact sensor will be degraded. On the other hand, if the end face of each of the heat sink and the contact sensor is protruded relative to the end face of each of the write head section and the read head section, the distance between the surface of the recording medium and the end face of each of the write head section and the read head section in the medium facing surface is not sufficiently small at the point in time at which the contact sensor has detected a contact. Consequently, in this case, the write characteristics of the write head section and the read characteristics of the read head section may deteriorate.
To address this problem, the inventors of this application contemplated forming the heat sink from a metal-based magnetic material as with the magnetic pole, a principal element of the write head section. This allows the amount of polishing of the heat sink in the step of forming the medium facing surface to be at the same level as that of the magnetic pole, thereby making it possible to avoid the aforementioned problem.
A heat sink formed of a metal-based magnetic material, however, may cause a magnetic field to occur from the end face of the heat sink located in the medium facing surface in a direction toward the recording medium. The magnetic field may adversely affect the recording medium or the write characteristics of the write head section.